Into which of the three elements of manufacturing cost would each of the following be classified?
a. Tubing used in manufacturing bicycles.
b. Wages paid by an automobile manufacturer to employees who test-drive completed automobiles.
c. Property taxes on machinery.
d. Gold bullion used by a jewelry manufacturer.
e. Wages of assembly-line workers who package frozen food.
f. Salary of plant superintendent.
g. Electricity used in factory operations.
h. Salary of a nurse in a factory first-aid station.